Control Valve Cv Calculator
Use the required liquid flow and pressure drop across the valve to estimate a coefficient. This is a first-pass calculation, not manufacturer sizing or a valve selection.
Sources: Spirax Sarco, Control Valve Sizing for Water Systems and Control Valve Capacity. https://www.spiraxsarco.com/learn-about-steam/control-hardware-electric-pneumatic-actuation/control-valve-sizing-for-water-systems · https://www.spiraxsarco.com/learn-about-steam/control-hardware-electric-pneumatic-actuation/control-valve-capacity
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A QUICK WALKTHROUGH
How to use this tool
- Enter liquid flow in m³/h, valve differential pressure in bar, and flowing density in kg/m³.
- Optionally enter pressure drop across the rest of the system in bar for a simple authority ratio.
- Calculate, review the boundary notes, and copy or download the report. Editing inputs clears the result.
Liquid equation and units
For an incompressible liquid under the simplified non-choked relationship: Kv = Q·√(SG/Δpbar), where Q is m³/h, Δpbar is positive bar across the valve, and SG = ρ/1000 using the entered kg/m³ density (water reference 1000 kg/m³). US Cv = 1.156·Kv. The result is a required coefficient at the entered condition, not a catalog rating or installed capacity guarantee.
Optional authority screen
If entered, authority a = Δpvalve/(Δpvalve + Δpsystem), with both drops in bar. This arithmetic omits dynamic system interaction and does not establish controllability or an acceptable authority target.
Strict scope
Liquid-only first-pass screen. No gas, vapor/steam, two-phase flow, flashing, cavitation, noise, viscosity correction, choking checks, piping reducers/fittings, valve recovery factors, temperature-dependent properties, actuator/trim sizing, or manufacturer-specific selection. Use the applicable IEC/ISA method, current manufacturer data and process conditions before selection.
Sources
Reference: Spirax Sarco, Control Valve Sizing for Water Systems (https://www.spiraxsarco.com/learn-about-steam/control-hardware-electric-pneumatic-actuation/control-valve-sizing-for-water-systems) and Control Valve Capacity (https://www.spiraxsarco.com/learn-about-steam/control-hardware-electric-pneumatic-actuation/control-valve-capacity). The reference covers coefficient units and authority concepts; this page deliberately omits the full IEC/ISA sizing corrections.
Local report
The calculation stays in this browser. The report includes raw and SI inputs, equations, result and scope notes. Any input edit clears the prior successful snapshot.
GOOD TO KNOW
Common questions
What do Kv and Cv mean here?
They are coefficient values calculated from your liquid flow, pressure drop and density inputs. They are not a selected valve size or a promise of actual performance.
Does the result check cavitation or flashing?
No. Vapor pressure, pressure recovery and manufacturer factors are not modeled.
Can I use this for gas or steam?
No. This calculator is limited to incompressible liquids.